Earth Notes - St. Elmo's Fire

Lightning is a given during the Colorado Plateau's summer monsoon season. But it's not the only kind of electricity that comes from the heavens.

St. Elmo's Fire is a peculiar phenomenon that infrequently, but memorably, shows up at the margins of thunderstorms. It forms when the atmosphere's highly charged electrical field comes into contact with grounded objects. As molecules in the air are ionized, they emit a bright blue, violet or green glow.

The electrical voltage required to induce the glowing discharge accumulates on sharp pointed objects, which is why the glow is most often seen on ships' masts, church spires, chimneys, and aircraft wings. It's perhaps most common at sea, where it lights up the masts, sails, and rigging of ships.

Hence the name St. Elmo is the patron saint of sailors. But ashore it can also illuminate plant leaves, and even the tips of cattle horns.

Flagstaff resident Stewart Aitchison has been hiking for more than 30 years, but has only seen the phenomenon once, in Grand Canyon. On that occasion a thunderstorm was moving in from the east as Aitchison and a friend descended the South Kaibab Trail.

Just below Cedar Ridge, they noticed little flashes of static flying off their boot soles. The desert plants were glowing, the prickly pear cactus outlined in an eerie, faint green light.

It only lasted a few moments before the rain came a reminder that keeping your eyes peeled pays off, whether you're at sea or out in the canyon country.